The invention is based on a priority application EP08290260.2 which is hereby incorporated by reference.
The invention relates to a method for monitoring a passive optical network (PON) having a tree-Like structure with a main line and a plurality of branches, to a monitoring unit connectable to a branch of a PON, and to a PON comprising at least one such monitoring unit.
In order to improve the quality of service of optical networks, in particular passive optical networks (PONs) with a tree-like structure, continuous monitoring techniques detecting and localizing faults are of special interest, as they are expected to provide substantial cost savings to telecommunications companies operating these networks.
However, due to the large distances which are covered by the fiber links of a PON, a network operator usually only has access to the network from the main line, in particular from an optical line termination, OLT, which is Located at a head end of the PON. For checking the functionality of the branches of the PON from the main line, it is known to dispose monitoring units in these branches which are usually arranged close to the location of the end users.
The downstream communication between the OLT and the monitoring units may be performed by the transmission of binary information including an identifier to a particular monitoring unit which may then execute a predefined function. In this respect, EP 1 037 417 B1 discloses a method for performing central control of an in-line element such as an optical amplifier or an optical switch in a tree-like network, wherein the OLT adds extra bits in predefined grants sent downstream to the in-line element. These extra bits comprise an identification of the in-line element and contain a locally predefined function for execution by the selected in-line element.
However, for performing central control in the way described above, the grant messages must be captured out of the downstream transmission, such that the in-line elements or further elements used for operation and maintenance have to listen permanently to the downstream transmissions for identifying and processing the grant messages.